Abstract

The goal of this thesis was to create a mouse model permitting the analysis of neuregulin-1 (NRG1) function in the adult nervous system. NRG1 is a polypeptide growth factor, which contains an ‘epidermal growth factor like’ (EGFL) domain and serves as a ligand for the erbB receptor tyrosine kinase family. Alternative splicing of the NRG1 gene gives rise to at least 15 NRG1 isoforms, which can be grouped into type I, II and III variants. NRG1 has been traditionally viewed as a growth factor important for development. However, recent studies have suggested a continuous requirement for NRG1 signaling in the mature animal. Thus far, the study of NRG1 function in vivo has been hampered by the early embryonic or perinatal death of complete and isoform-specific null mutants. To overcome the limitations of the available mouse mutants, the tetracycline regulated gene expression system (Tet-System) was utilized in this thesis. NRG1 is expressed by virtually all cholinergic neurons, therefore the choline acetyltransferase (ChAT) gene was selected to direct the expression of the tetracycline-dependent transactivator (tTA2S) to cholinergic neurons. In order to increase the likelihood that all required regulatory elements were present, a bacterial artificial chromosome (BAC), roughly 200kb in size, containing the ChAT gene and flanking sequences was used. Homologous recombination in bacteria was used to insert the tTA2S cDNA into the ChAT gene. The resulting ChAT-tTA2S BAC construct was used for the generation of transgenic animals by oocyte injection. The ChAT-tTA2S transgenic mice were subsequently characterized by in situ hybridization and by mating them to reporter mice carrying a tTA-inducible ?-galactosidase gene. In two independent transgenic founder lines, a faithful cholinergic expression was observed. In addition, mouse lines for the tTA-inducible expression of NRG1 isoforms were generated. Their functionality was assessed by mating them to the ?-CaMKII-tTA mice, in which tTA expression is directed to principal neurons of the forebrain. One mouse line was identified that showed a tight doxycyline-dependent regulation of transgene-derived NRG1 type I mRNA expression. Through the use of ChATtTA:NRG1 type I doubly transgenic animals, it is now possible to examine the effects of increased NRG1 type I expression on synaptic function and myelination in the mature nervous system. Moreover, the ChATtTA transgenic mouse lines that have been generated are universal tools to regulate the expression of any transgene of interest in cholinergic cells.